Head lice are insects without wings. They live on people's heads and feed on their blood. They are a type of parasite. An adult is called a louse and is 2-3 mm long, or about the size of a sesame seed. Head lice eggs, which are called nits, are even smaller. The eggs look almost like a dandruff flake. Lice and nits are easiest to detect at the neckline and behind the ears. A female louse produces about 100 eggs.